It is known to dimension semiconductor components, in particular power transistors, in such a way that their activatable power greatly exceeds the ordinarily permissible continuous demands and the continuous losses which thereby occur. The semiconductor elements can thus be produced more economically, since they do not need to be designed for continuous operation at the activatable power. It is known to associate with the semiconductor components protective circuits which can be activated as a function of a component temperature of the component, so that damage to the components due to extended continuous load--for which they are not designed--can be prevented.
Known for this purpose are circuit arrangements in which the semiconductor component is switched off when a limit temperature is exceeded. The power transistor is switched off, in this context, by means of a measurement of forward voltage or off-state current at integrated sensor elements which correspondingly trigger the semiconductor component. Reference is made here to Tietze and Schenk, 9th edition, page 523.
DD Patent 228 835 discloses an integrated overtemperature protection circuit arrangement in which bipolar transistors are connected together in such a way that a base-emitter voltage of one transistor is acted upon by a hysteresis, such that with the transistor in the "on" state, a working current is modified by the use of a current level in such a way as to dissipate a current which is less than the working current and is always at a constant ratio to it. This causes the power transistor to be switched on or off as a function of temperature. It is not possible to modulate the power dissipation without switching off. Another disadvantage is that this circuit can be used only in temperature ranges up to approx. 150 degrees C. A semiconductor switch having an overtemperature protector which has a temperature-sensitive element is known from GB-A 2 234 112. The temperature-sensitive element is configured in the form of a diode switched into the off-state direction, and allows the driver current of the semiconductor switch to be shunted if the latter becomes too hot.